s/gpr_slice/grpc_slice, and move around tests, impls

Makefile

build.yaml

grpc.def

include/grpc++/impl/codegen/core_codegen.h

include/grpc++/impl/codegen/core_codegen_interface.h

include/grpc++/impl/codegen/proto_utils.h

include/grpc++/impl/codegen/thrift_serializer.h

include/grpc++/support/slice.h

include/grpc/byte_buffer.h

include/grpc/impl/codegen/gpr_types.h

include/grpc/impl/codegen/grpc_types.h

include/grpc/impl/codegen/slice.h

include/grpc/slice.h

include/grpc/slice_buffer.h

src/core/ext/client_channel/connector.h

src/core/ext/client_channel/default_initial_connect_string.c

src/core/ext/client_channel/http_connect_handshaker.c

src/core/ext/client_channel/initial_connect_string.c

src/core/ext/client_channel/initial_connect_string.h

src/core/ext/client_channel/subchannel.c